Plesk 8.6 says Backup service unavailable

[allank]

Running on a VSP at NetSol, trying to create a backup of a site under a specific domain. I select the domain, and then click Backup. After a few seconds I get:

Service is not available now, probably your Plesk is misconfigured.
Contact Your provider for details.

Internal Plesk error occurred:

No error number or other hint as to what is happening. Since this is a VPS, NetSol will not provide ANY technical support, and I can't find anything in Plesk, or any other part of the VPS that refers to a backup service. Everything else is working fine. I tried rebooting the VPS, nada.

Does anyone have any ideas on this? Any help will be greatly appreciated.

Cheers,
Allan